--- old/src/hotspot/os/linux/gc/z/zPhysicalMemoryBacking_linux.cpp	2020-05-18 16:30:50.186874711 +0200
+++ new/src/hotspot/os/linux/gc/z/zPhysicalMemoryBacking_linux.cpp	2020-05-18 16:30:49.929866386 +0200
@@ -112,9 +112,8 @@
 static int z_fallocate_hugetlbfs_attempts = 3;
 static bool z_fallocate_supported = true;
 
-ZPhysicalMemoryBacking::ZPhysicalMemoryBacking() :
+ZPhysicalMemoryBacking::ZPhysicalMemoryBacking(size_t max_capacity) :
     _fd(-1),
-    _size(0),
     _filesystem(0),
     _block_size(0),
     _available(0),
@@ -126,6 +125,13 @@
     return;
   }
 
+  // Truncate backing file
+  if (ftruncate(_fd, max_capacity) == -1) {
+    ZErrno err;
+    log_error(gc)("Failed to truncate backing file (%s)", err.to_string());
+    return;
+  }
+
   // Get filesystem statistics
   struct statfs buf;
   if (fstatfs(_fd, &buf) == -1) {
@@ -361,10 +367,6 @@
   warn_max_map_count(max);
 }
 
-size_t ZPhysicalMemoryBacking::size() const {
-  return _size;
-}
-
 bool ZPhysicalMemoryBacking::is_tmpfs() const {
   return _filesystem == TMPFS_MAGIC;
 }
@@ -379,18 +381,6 @@
   return access(ZFILENAME_SHMEM_ENABLED, R_OK) == 0;
 }
 
-ZErrno ZPhysicalMemoryBacking::fallocate_compat_ftruncate(size_t size) const {
-  while (ftruncate(_fd, size) == -1) {
-    if (errno != EINTR) {
-      // Failed
-      return errno;
-    }
-  }
-
-  // Success
-  return 0;
-}
-
 ZErrno ZPhysicalMemoryBacking::fallocate_compat_mmap_hugetlbfs(size_t offset, size_t length, bool touch) const {
   // On hugetlbfs, mapping a file segment will fail immediately, without
   // the need to touch the mapped pages first, if there aren't enough huge
@@ -489,41 +479,13 @@
   // since Linux 4.3. When fallocate(2) is not supported we emulate it using
   // mmap/munmap (for hugetlbfs and tmpfs with transparent huge pages) or pwrite
   // (for tmpfs without transparent huge pages and other filesystem types).
-
-  const size_t end = offset + length;
-  if (end > _size) {
-    // Increase file size
-    const ZErrno err = fallocate_compat_ftruncate(end);
-    if (err) {
-      // Failed
-      return err;
-    }
-  }
-
-  // Allocate backing memory
-  const ZErrno err = ZLargePages::is_explicit()
-                     ? fallocate_compat_mmap_hugetlbfs(offset, length, false /* touch */)
-                     : (ZLargePages::is_transparent()
-                        ? fallocate_compat_mmap_tmpfs(offset, length)
-                        : fallocate_compat_pwrite(offset, length));
-
-  if (err) {
-    if (end > _size) {
-      // Restore file size
-      fallocate_compat_ftruncate(_size);
-    }
-
-    // Failed
-    return err;
-  }
-
-  if (end > _size) {
-    // Record new file size
-    _size = end;
+  if (ZLargePages::is_explicit()) {
+    return fallocate_compat_mmap_hugetlbfs(offset, length, false /* touch */);
+  } else if (ZLargePages::is_transparent()) {
+    return fallocate_compat_mmap_tmpfs(offset, length);
+  } else {
+    return fallocate_compat_pwrite(offset, length);
   }
-
-  // Success
-  return 0;
 }
 
 ZErrno ZPhysicalMemoryBacking::fallocate_fill_hole_syscall(size_t offset, size_t length) {
@@ -534,12 +496,6 @@
     return errno;
   }
 
-  const size_t end = offset + length;
-  if (end > _size) {
-    // Record new file size
-    _size = end;
-  }
-
   // Success
   return 0;
 }